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Benchmark DAC1's XLR driving headphones--great results

post #1 of 122
Thread Starter 
Some head-fiers have reported that Benchmark DAC1's balanced (XLR) out can drive Senn 580/600/650 series headphones very well (DAC1 has preamp function so the volume knob controls XLR output level). I have to thank Neilpeart for discussions about using the XLR out as a headphone amp instead of the built-in headphone amp in DAC1.
DAC1 has one internal headphone amp driving two headphone jacks on the front panel. It uses NE5532 opamps to drive BUF634 output buffers. This is a very high current headphone amp capable of driving even the monstrous K1000 to a usable level. Neilpeart has commented that its quality is roughly equivalent to a basic PIMETA, which I have not heard personally.
The first question that comes to my mind of using XLR to drive headphones is whether it has enough current output. HD650 (300 ohm, 97 dB/mW) is a hard-to-drive headphone, but XLR drives it well. K501 (120 ohm, 94 dB/mW) is even harder to drive, current-wise. The XLR can output >20 dBu voltage, so the high voltage demand of high impedance phones is not a problem. The question is the current demand. Surprisingly, XLR also drives K501 very well, without signs of weak bass, compressed dynamics or clipping.
The second question is the damping factor. XLR output, when bridged to unbalanced mode, has 30 ohm impedance. For a 120 ohm load, the damping factor is only 4. After I look up the impedance curve of K501 on headroom.com, a simple calculation showed that the impedance bump of K501 is not large enough to alter the frequency response curve to any appreciable amount. In fact , XLR produces better bass response on K501 than the zero ohm headphone jack.
Based on these technical considerations and listening tests, I conclude that XLR out of DAC1 can drive almost all headphones satisfactorily except for the "super low efficiency" studio headphones. In fact, few headphones have higher current demands than K501. As for lower impedance (<120 ohm) phones like HD280, DT250, RS-1, ER-4P, CD3000 and SR-60, they all have pretty flat impedance curves so that low dmaping factor is not an issue. Taken together, I believe DAC1's XLR out will drive most of the high-end headphones commonly discussed here.

Next question is: how to drive headphones using XLR output?
IMO the easiest solution is to get these two adapters:
http://www.sweetwater.com/store/detail/GXF132/
http://www.sweetwater.com/store/detail/YMR197/
The first one is XLR to RCA adapter (pin2 to hot; pin1 and pin3 to ground). Neilpeart and I both connect the XLR pins to RCA this way and it seems to work fine, although another option is to leave pin3 floating.
The second adapter truns L/R RCA signal to a female 1/8 plug, making L/R channles share a common ground.
Sweetwater.com offers free shipping, so for $23 you can start using any headphone with a 1/8 plug with DAC1's XLR put.

So far I have established that most headphones out there can be easily used with XLR out of DAC1, what about the sonic benefits?
Neilpart and other Senn 6xx users have already said that DAC1's XLR sounds even better than its headphone jack. Is this a special case or a general rule?
After testing with K501 I would say that it is a general rule that XLR sounds better than headphone out on DAC1.
The sonic benefits of using the XLR reminds me very much of going from CD to SACD. The improvements are smoother highs with more airiness, more rounded transients with better rhythm, and stronger bass with less booming. In instrument terms this translates to a fuller and more resonant violin sound, a crisper piano sound with a more natural decay, and a faster drum sound with more impact. The difference is not huge, but quite noticeable. Going from headphone jack to XLR offers about 50% improvement compared to going from CD to SACD on my Sony player. I would personally call that s significant improvement.

Incidentally, Neilpeart and I both feel that lifting the safety ground prong of DAC1's powercord makes it sound better. I don't know if this becuase the safety ground of my house is not clean or something.

In conclusion, I think DAC1's XLR output drives headphones better than its headphone amp. Its headphone amp by itself is not bad either, but XLR is just a step up. Connecting DAC1 to Sonic Impact T-amp and speakers, I also feel XLR also sounds better than RCA out. Since XLR-to-RCA adapters are inexpensive, DAC owners ought to give it a shot.
post #2 of 122
You mention lifting the safety ground prong of DAC1's powercord to make it sound better. I have a bit of edginess to my DAC1->XLR'd 650s that I'm still trying to chase down and still suspect dirty power in the old three family I live in.

By "lifting" do you mean take a pair of pliers and just yank the ground lug out of the power cord?

Thx!
post #3 of 122
Quote:
Originally Posted by Ferbose
The first one is XLR to RCA adapter (pin2 to hot; pin1 and pin3 to ground). Neilpeart and I both connect the XLR pins to RCA this way and it seems to work fine, although another option is to leave pin3 floating.
The second adapter truns L/R RCA signal to a female 1/8 plug, making L/R channles share a common ground.
Sweetwater.com offers free shipping, so for $23 you can start using any headphone with a 1/8 plug with DAC1's XLR put.
Hi Ferbose, you'll have to excuse my electrical ignorance, but this is interesting to me for the more common, non-headphone purpose of an XLR to RCA interconnect from the DAC1 to an integrated amp.
It seems the principle is the same between our two different purposes?
Do you think there could be some sonic advantages were I to use an XLR to RCA cable rather than RCA to RCA?
Thanks
post #4 of 122
Just wanted to chime in on the HD650 XLR-driven setup with DAC1; I had Larry build me a headphile V2 senn cable with female XLR's and I'm currently using it with the DAC1 outta the XLRs. The sound upgrade compared with standard headphone out in front is huge; bass literally slams, soundstage is wider but most remarkably seems to have more depth, highs sparkle (after about 100hrs of cable burn-in; new cable sounded a bit edgy/harsh). I wonder if Ferbose's approach with XLR/rca adapters will sound good with my standard 1/4 connector-equipped Zu cable; I may have to try it out.

Anyone who has a DAC1 and Senn's should try the XLR approach one way or another, it's remarkable.

One important word of warning: the unattenuated output of the XLR jacks(that is, with the switch in the back of the DAC1 set to "calibrated" rather than variable) is dangerously loud and certainly can potentially trash your ears and cans if one is not careful.

I use the calibrated setting with Foobar in conjunction with Foobar's digital volume attenuation (usually set to -33 up to -20 DB depending on the tune); this seems to sound a little better than the variable setting using the DAC1's pot, but remember, if you're surfing the web while listening and some annoying ad pops up and starts playing music without the benefit of Foobar's attenuation, your ears will bleed and cans crackle . I imagine this caution should be applied to any cans used in this fashion.
post #5 of 122
I'm not too sure about this, but isn't the reason the 650s sound good out of the DAC1 because they are balanced? If you use the XLR female to female RCA -> 2 rca to 1/4" don't you almost defeat the purpose?

Also has anyone compared the DAC1 Balanced outs to say RCA outs and a dynahi?
post #6 of 122
Quote:
Originally Posted by zdogg
One important word of warning: the unattenuated output of the XLR jacks(that is, with the switch in the back of the DAC1 set to "calibrated" rather than variable) is dangerously loud and certainly can potentially trash your ears and cans if one is not careful.

I use the calibrated setting with Foobar in conjunction with Foobar's digital volume attenuation (usually set to -33 up to -20 DB depending on the tune); this seems to sound a little better than the variable setting using the DAC1's pot, but remember, if you're surfing the web while listening and some annoying ad pops up and starts playing music without the benefit of Foobar's attenuation, your ears will bleed and cans crackle . I imagine this caution should be applied to any cans used in this fashion.
I have also found the calibrated mode to sound better, and also use the foobar digital attenuator, to about the same values. You can get rid of the latter problems by setting a second or onboard soundcard as the default in windows, so the DAC1 will only play back foobar sounds.
post #7 of 122
Thread Starter 
Quote:
Originally Posted by drp
By "lifting" do you mean take a pair of pliers and just yank the ground lug out of the power cord?
Thx!
Using a three-to-two prong adapter is the easiest way.
post #8 of 122
Thread Starter 
Quote:
Originally Posted by eyeteeth
Hi Ferbose, you'll have to excuse my electrical ignorance, but this is interesting to me for the more common, non-headphone purpose of an XLR to RCA interconnect from the DAC1 to an integrated amp.
It seems the principle is the same between our two different purposes?
Do you think there could be some sonic advantages were I to use an XLR to RCA cable rather than RCA to RCA?
Thanks
RCA output has 1250 ohms impedance, XLR is 30 ohms when converted to RCA.
Depending on your downstream amplifier, the impedance difference may or may not cause a sonic difference.
But some DAC1 users think XLR just sounds better than RCA out in the first place.
I have not yet found my own answer to whether XLR-to-RCA always sounds better than built-in RCA.
Of course built-in RCA can't properly drive headphones because impedance is way high.
post #9 of 122
Thread Starter 
Quote:
Originally Posted by Natsuiro
I'm not too sure about this, but isn't the reason the 650s sound good out of the DAC1 because they are balanced? If you use the XLR female to female RCA -> 2 rca to 1/4" don't you almost defeat the purpose?

Also has anyone compared the DAC1 Balanced outs to say RCA outs and a dynahi?
I hope I get the whole thing right.

///EDITED
Balanced connnection for line out:
L Connector: pin2 signal, pin3 inverted signal, pin1 ground
R Connector: pin2 signal, pin3 inverted signal, pin1 ground
/// END OF EDIT

Unbalanced connection for line out:
L connector: center signal, barrel ground
R connector: center signal, barrel ground

Balanced headphone connector
L channel: pin1 signal, pin2 ground
R channel: pin1 signal, pin2 ground

Normal headphone jack:
Tip: left signal
Ring: right signal
Sleeve: shared ground

So balanced headphone connection actually matches unbalanced line out.
May be there is some disadvantage to having Land R channels share a common ground wire in headphone jacks.
But since headphone jacks have always been like that I would imagine whatever disadvantage there may be would be very, very small.
For headhone cables there is much higher current than line-out cables, so I guess EM interference is much less of an issue.
I guess the main benefit of using XLR out is that its sound quality is intrisically better than the headphone jack on DAC1, not really becuase of 4-conductor vs 3-conductor difference.
post #10 of 122
Quote:
Originally Posted by Ferbose
Using a three-to-two prong adapter is the easiest way.
Excellent; thank you. I have the Apogee in hand (came in today) and will get the gnd plug adaptor (or doctor another pwr cable) before A-Bing the Mini and the DAC1.

At work at the monment, listening to the Mini-DAC with XLR'd 650 thru a D555. Balanced, smooth, and transparent. Very nice DAC.

Noticed your conversion wiring comment. Think I have the pieces to build an XLR to phono plug adaptor.
post #11 of 122
Quote:
Originally Posted by Ferbose
I hope I get the whole thing right.

Balanced connnection for line out:
L Connector: pin1 signal, pin2 inverted signal, pin3 ground
R Connector: pin1 signal, pin2 inverted signal, pin3 ground

Unbalanced connection for line out:
L connector: center signal, barrel ground
R connector: center signal, barrel ground

Balanced headphone connector
L channel: pin1 signal, pin2 ground
R channel: pin1 signal, pin2 ground

Normal headphone jack:
Tip: left signal
Ring: right signal
Sleeve: shared ground

So balanced headphone connection actually matches unbalanced line out.
May be there is some disadvantage to having Land R channels share a common ground wire in headphone jacks.
But since headphone jacks have always been like that I would imagine whatever disadvantage there may be would be very, very small.
For headhone cables there is much higher current than line-out cables, so I guess EM interference is much less of an issue.
I guess the main benefit of using XLR out is that its sound quality is intrisically better than the headphone jack on DAC1, not really becuase of 4-conductor vs 3-conductor difference.

According to the DAC1 manual, the XLR pinout is:
Pin 1 is ground
Pin 2 is the positive signal
Pin 3 is the negative signal

Shorting Pin 3 to ground will cause very high levels of distortion.
(Don't use the adapter that connects pin 3 to ground.)

A balanced headphone connection would use Pin 2 and 3.
post #12 of 122
Quote:
Originally Posted by Ferbose
RCA output has 1250 ohms impedance, XLR is 30 ohms when converted to RCA.
Depending on your downstream amplifier, the impedance difference may or may not cause a sonic difference.
But some DAC1 users think XLR just sounds better than RCA out in the first place.
I have not yet found my own answer to whether XLR-to-RCA always sounds better than built-in RCA.
Of course built-in RCA can't properly drive headphones because impedance is way high.
I learned from a search at Audio Asylum that the unbalanced (RCA) output of the DAC1 is currently 30 ohm output impedance.

According to the downloadable DAC1 manual available at the Benchmark site, the PCB revision date was 11/22/04.

Best,
Beau

Edit: Misreading of manual resulted in incorrect date in original of this post. Thanks to dip16amp for the correction.
post #13 of 122
Quote:
Originally Posted by Beauregard
I learned from a search at Audio Asylum that the unbalanced (RCA) output of the DAC1 is currently 30 ohm output impedance.

According to the downloadable DAC1 manual available at the Benchmark site, this change was effective 3/1/04.

Best,
Beau
It's in the REV H manual 11/22/04 as PCB REV F has 30 ohms. The PCB REV C has them as 1250 ohms.
post #14 of 122
Thread Starter 
Quote:
Originally Posted by dip16amp
According to the DAC1 manual, the XLR pinout is:
Pin 1 is ground
Pin 2 is the positive signal
Pin 3 is the negative signal

Shorting Pin 3 to ground will cause very high levels of distortion.
(Don't use the adapter that connects pin 3 to ground.)

A balanced headphone connection would use Pin 2 and 3.
Yes you are right.
I was wrong in my previous post. Pin 1 of XLR is ground.
For DAC1, it says pin 1 ground is connected to chasis.
I guess chasis is in turn connected to safety gorund, that is the third prong in power cord connected eventually to actaul earth.
But I lifted the safety ground in the power cord anyway.
The adapter I use does short circuit the output of each pin 3.
According to the manual this would cause high distortion.
And in my case the short circuits are not really connected to earth outside the house.
This configuration looks pretty messed up but I can't detect any detrimental effect.
According to what Neilpaeart told me, he also shorts pin 3 and lifts safety ground (earth) in power cord.
If safety gorund in powercord is not lifted, the sound seems a tiny bit less detailed, and there is no major change.
Using XLR to 1/8 jack conversion to drive my speaker amp (Sonic Impact), I also detect no deleterious effect. In fact it sounds better than unbalanced RCA output. I should mention that my amplifier for speaker system is connected to DC battery. I don't know if this matters.
Anyway, even if there is some distortion caused by shorting pin 3, it is probably so small htat I can't recognize it.

Has anyone tried using XLR to drive headphone while lifting pin 3?
post #15 of 122
Actually, my balanced Zu Mobius I'm using now lifts pin 3 rather than shorts it (according to Zu). The balanced modification is worth the effort (the sound is so clear and powerful), and lifting the ground from the power cord (or removing the removable ground pin from my PS Audio Plus cable, in my case) does make a difference, as all Benchmark DAC1s I have tested have the same grounding issue. Morsel can explain this particular issue further if required.
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